U.S. patent number 5,105,783 [Application Number 07/632,229] was granted by the patent office on 1992-04-21 for digital ignition system.
This patent grant is currently assigned to Allied-Signal Inc.. Invention is credited to Jeffrey E. Folts, Stephen H. Nussbaum.
United States Patent |
5,105,783 |
Nussbaum , et al. |
April 21, 1992 |
Digital ignition system
Abstract
A method of and apparatus for enabling at least one spark plug
of a internal combustion engine to provide a fuel igniting spark at
a selectable time in the engine cycle is disclosed. Sensors provide
a first engine rotation determined pulse train the repetition rate
of which is the same as the number of revolutions per second of the
engine and a second engine rotation determined pulse train the
repetition rate of which is an integral multiple of that of the
first pulse train. The reference pulse initiates a count of pulses
in the second pulse train and, upon reaching a preselected count,
initiates a count of pulses in a third independent pulse train
having a much greater repetition rate. The spark plug is enabled
when the third pulse train count reaches a preselected count. In
the event the engine is a multi-cylinder engine having at least one
spark plug for each cylinder, the pulses in the second pulse train
are counted up to different preselected counts for different
cylinders and a different spark plug is enabled for each different
preselected count.
Inventors: |
Nussbaum; Stephen H. (Temecula,
CA), Folts; Jeffrey E. (San Diego, CA) |
Assignee: |
Allied-Signal Inc. (Morristown,
NJ)
|
Family
ID: |
24534640 |
Appl.
No.: |
07/632,229 |
Filed: |
December 20, 1990 |
Current U.S.
Class: |
123/335; 123/625;
123/406.63; 701/102; 123/643 |
Current CPC
Class: |
F02P
15/12 (20130101); F02P 5/15 (20130101); Y02T
10/46 (20130101); Y02T 10/40 (20130101) |
Current International
Class: |
F02P
15/12 (20060101); F02P 15/00 (20060101); F02P
5/15 (20060101); F02P 015/12 (); F02P 005/15 ();
F02D 017/00 () |
Field of
Search: |
;123/335,416,417,609,424,643,625 ;364/431.04 ;324/384 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Argenbright; Tony M.
Attorney, Agent or Firm: McCormick, Jr.; Leo H. Palguta;
Larry J. Walsh; Robert A.
Claims
We claim:
1. The method of enabling at least one spark plug of an internal
combustion engine to provide a fuel igniting spark at a selectable
time in the engine cycle comprising:
providing a first engine rotation determined pulse train the
repetition rate of which is the same as the number of revolutions
per second of the engine, whereby a pulse is provided which is
indicative of engine crankshaft position;
providing a second engine rotation determined pulse train the
repetition rate of which is an integral multiple of that of the
first pulse train, whereby a series of pulses is provided
indicative of engine speed;
providing a third pulse train the repetition rate of which is
significantly higher than that of the second pulse train, the
repetion rate of the third pulse train being independent of engine
rotation;
utilizing the reference pulse to initiate a count of pulses in the
second pulse train and, upon reaching a preselected count,
initiating a count of pulses in the third pulse train; and
enabling the spark plug when the third pulse train count reaches a
preselected count.
2. The method of claim 1 wherein the engine is a multi-cylinder
engine having at least one spark plug for each cylinder, the step
of utilizing counting the pulses in the second pulse train to
different preselected counts for different cylinders, the enabling
step enabling a different spark plug for each different preselected
count.
3. The method of claim 1 including the additional step of storing
at least two different desired values for the third pulse train
preselected count, each indicative of a desired time for enabling
the spark plug, the step of enabling including the step of
selecting a desired one of the two stored values.
4. The method of claim 1 including the additional step of manually
modifying the preselected count of third pulse train pulses to
thereby optionally manually fine-tune the time at which the spark
plug is enabled.
5. The method of claim 1 wherein the step of enabling includes
sensing the repetition rate of the second pulse train and
determining the preselected count at which the spark plug is to be
enabled in accordance with the sensed rate thereby varying ignition
as a function of engine speed.
6. The method of claim 1 further comprising the step of
preselecting an overspeed threshold repetition rate beyond which it
is undesirable to operate the engine, continuously monitoring one
of the first and second pulse trains, and initiating corrective
action when the repetition rate of the monitored pulse train
exceeds the overspeed threshold repetition rate.
7. The method of claim 1 wherein the step of enabling the spark
plug when the third pulse train count reaches a preselected count
includes the step of extending the time during which the spark plug
is enabled when starting the engine so as to provide a spark of
longer duration during start-up and spark of shorter duration
during normal running.
8. An internal combustion engine microprocessor based ignition
system which allows a more precise setting of the ignition timing
to more precisely control the point in the engine cycle at which
ignition occurs comprising:
a first engine crankshaft rotation sensor for providing a first
pulse train the repetition rate of which is the same as the number
of revolutions per second of the engine, whereby a pulse is
provided which is indicative of engine crankshaft position;
a second engine crankshaft rotation sensor for providing a second
pulse train the repetition rate of which is an integral multiple of
the first pulse train, whereby a series of pulses is provided
indicative of engine speed;
means for providing a third pulse train the repetition rate of
which is significantly higher than that of the second pulse train,
the repetition rate of the third pulse train being independent of
engine rotation;
digital circuitry responsive to the reference pulse to initiate a
count of pulses in the second pulse train and, upon reaching a
preselected count, to initiate a count of pulses in the third pulse
train; and
means for storing a desired value of the third pulse train count
indicative of the desired time of ignition in the engine cycle;
and
means causing ignition when the third pulse train count reaches the
stored desired value
9. The internal combustion engine microprocessor based ignition
system of claim 8 further comprising means for storing a second
desired value of the third pulse train count indicative of a second
desired time of ignition in the engine cycle, and means for
optionally replacing the desired value with the second desired
value to determine the time of ignition in the engine cycle.
10. The internal combustion engine microprocessor based ignition
system of claim 8 wherein the engine is a multi-cylinder engine
having at least one spark plug for each cylinder, the digital
circuitry reaching a different preselected count of pulses in the
second pulse train for each different cylinder, the means causing
ignition enabling a different spark plug for each different
preselected count.
11. The internal combustion engine microprocessor based ignition
system of claim 8 further comprising an optional manual control for
modifying the desired value of the third pulse train count to
fine-tune the ignition timing if necessary.
12. The internal combustion engine microprocessor based ignition
system of claim 8 further comprising means for storing a first
selected running spark duration indicative value, means for storing
a second value indicative of a selected engine speed at which it is
desired to change spark duration, and comparison means for
comparing engine speed as indicated by one of the first and second
pulse trains with the second stored value and providing an
indication when the compared values are equal, the means for
causing ignition providing a maximum duration spark at engine
start-up and responding an indication from the comparison means to
reduce the spark duration to that indicated by the first stored
value.
13. The internal combustion engine microprocessor based ignition
system of claim 8 further comprising an analog signal source for
providing a signal the magnitude of which is indicative of a
desired amount of spark retardation, analog to digital converter
for converting the analog signal to an appropriately scaled digital
signal, and means for adding the appropriately scaled digital
signal to the stored desired value of the third pulse train count
and supplying the sum to the means causing ignition when the third
pulse train count reaches the stored desired value thereby delaying
time of ignition in the engine cycle.
14. The internal combustion engine microprocessor based ignition
system of claim 13 further comprising means for storing a second
desired value of the third pulse train count indicative of a second
desired time of ignition in the engine cycle, and means for
optionally replacing the desired value with the second desired
value to determine the time of ignition in the engine cycle.
15. The internal combustion engine microprocessor based ignition
system of claim 14 further comprising display means for cyclically
repeatedly displaying each of a plurality of different engine
operating parameters including the commanded angle at which
ignition occurs, the current engine RPM, which of the desired or
second desired values currently controls engine ignition, and a
measure of the spark retardation indicative analog signal.
Description
The present invention relates generally to apparatus methods and
processes for controlling the ignition timing in a spark ignited
internal combustion engine and more particularly to a
microprocessor based ignition system for such engines, particularly
large industrial engines.
Current ignition systems are cumbersome, somewhat inaccurate, and
not readily adaptable to the use of different fuels in the same
engine. Current ignition systems do not provide dependable
overspeed protection.
Among the several objects of the present invention may be noted the
provision of a readily programmed microprocessor based ignition
control system; the provision of a microprocessor based ignition
system having overspeed protection with programmable options for
warning or shutdown; the provision of a microprocessor based
ignition system which provides precise ignition pulse timing
predicted on a two stage counting process where gross pulses are
counted and thereafter much higher repetition rate clock pulses are
counted during the final countdown to ignition; the provision of an
ignition system where virtually all of the engine operating
parameters are easily programmed into the system so that the same
ignition unit may be adapted to engines having, for example,
different numbers of cylinders, different ignition timing
requirements for start-up as well as varying load conditions when
running, varying fuels, and either two or four-stroke-cycle
operation; the provision of either two or four-stroke-cycle
operation without the need for a separate camshaft reference signal
sensor; and the provision of an automatic microprocessor based
ignition control system having optional manual control to fine-tune
the ignition timing if necessary.
The present invention allows a more precise setting of the ignition
timing which in turn allows for more optimum engine operation
since, e.g., a greater spark advance may be provided when needed
while minimizing detonation thereby reducing engine damage or
maintenance requirements.
It is therefor a specific object of the present invention to more
precisely control the point in the engine cycle at which ignition
occurs than was heretofor possible. These as well as other objects
and advantageous features of the present invention will be in part
apparent and in part pointed out hereinafter.
In general, an internal combustion engine microprocessor based
ignition system which allows a more precise setting of the ignition
timing to more precisely control the point in the engine cycle at
which ignition occurs has first and second crankshaft rotation
sensors for providing a first pulse train the repetition rate of
which is the same as the number of revolutions per second of the
engine, and a second pulse train the repetition rate of which is an
integral multiple of the first pulse train whereby a reference
pulse is provided which is indicative of engine crankshaft position
and a series of pulses is provided indicative of engine speed. An
independent third pulse train the repetition rate of which is
significantly higher than that of the second pulse train is
generated, for example, by an internal clock, and digital circuitry
responds to the reference pulse to initiate a count of pulses in
the second pulse train and, upon reaching a preselected count, to
initiate a count of pulses in the third pulse train. A desired
value of the third pulse train count which is indicative of the
desired time of ignition in the engine cycle is preprogrammed into
the system and when the third pulse train count reaches the stored
desired value, ignition occurs.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1A-1C are a schematic block diagram of an engine and ignition
control system according to the present invention in one form;
FIGS. 2A-2C are a more detailed schematic block diagram of the
ignition control portion of the system of FIG. 1; and
FIGS. 3A, 3B, 3C and 3D illustrate the pulse trains utilized in
accurately determining the time of ignition.
Corresponding reference characters indicate corresponding parts
throughout the several views of the drawing.
The exemplifications set out herein illustrate a preferred
embodiment of the invention in one form thereof and such
exemplifications are not to be construed as limiting the scope of
the disclosure or the scope of the invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, the engine 12 has a crankshaft 14 supporting a flywheel
16 and, optionally, a toothed gear wheel 18. The flywheel 16 may
have a uniformly spaced set of holes or studs such as 32 and 34
which pass adjacent a first sensor 27 as well as a single hole or
stud 36, the passage of which is detected by sensor 29, to provide
a reference pint such as the beginning of each revolution, e.g.,
top dead center for a specific piston. This reference pulse from
sensor 29 may be used as a counter reset pulse. The pulse from
sensor 29 does not directly reset a counter. The pulse generates an
interrupt to the microprocessor which, in turn, responds by
presetting the NC counter with a calculated value determined by the
particular application the NC counter increments the value that the
TDCREF interrupt process preset into it every time an NC pulse is
detected. This counting continues until the count overflows which
overflow will occur at a consistent angular position on the
flywheel for every qualified TDCREF pulse occurrence thus
maintaining synchronism between the NC counter and the flywheel.
The TDCREF pulse on line 40 should occur every revolution for
two-stroke-cycle engines and for four-stroke-cycle engines, the
TDCREF is qualified by the CAMREF pulse on line 31. In the
four-stroke-cycle case, every other TDCREF pulse is used, namely
the ones which are coincident with the CAMREF pulses. The CAMREF
input on line 31 may occur more or less frequently than with every
other TDCREF pulse so long as coincidence between the two occurs
when a reference cylinder is at the top of the compression
stroke.
Each time the NC counter overflows, the microprocessor uses the
internal timer for precise measurement to the firing point and when
reached, it will turn on the appropriate ignition driver causing a
spark at the proper plug. The NC counter is preset after each
overflow with a value that corresponds to the next closest point on
the flywheel in NC increments prior to the next firing point. Once
reached, the microprocessor will use the internal timer to measure
in time (as opposed to crankshaft motion) from the overflow pint to
the actual firing point of the plug.
The TDCREF pulse on line 40, in theory, need only occur one time
after which the normal process of reloading the NC counter is
automatic every time the counter overflows and should stay in
synchronism with the flywheel if the NC input pulse train maintains
perfect integrity from revolution to revolution. The TDCREF pulse
provides a means of re-synchronizing the NC counter to the flywheel
on every occurrence in the two-stroke-cycle case or on every
occurrence that is coincident with the CAMREF pulse in the case of
four-stroke-cycle operation. The TDCREF pulse also provides a check
of the integrity of the NC pulse train. The total NC count since
the previous TDCREF Pulse may be evaluated and, if out of
tolerance, a fault indication initiated.
Magnetic or optical sensors detecting the passage of holes such as
32, 34 and 36, or the passage of teeth on a gear 16 as well as reed
switches or a host of other techniques may be utilized to provide
pulse trains indicative of engine speed and crank shaft angular
position. An illustrative pulse train generated by sensor 29 is
shown in FIG. 3b and appears on line 40 while one from sensor 27
appears on line 42 and is shown in FIG. 3c, and one from sensor 38
appears on line 31 is shown as FIG. 3a. The engine 12 is typically
a large multi-cylinder engine having at least one spark plug such
as 20 for each cylinder. Each spark plug such as 20, 22 or 24 may
have associated therewith its own individual step-up transformer
such as 26, 28 or 30 which receive timed capacitor discharge pulses
on their respective inputs to fire the spark plugs.
The microprocessor based ignition control utilizes primarily CMOS
type components centered around a Motorola 68HC11 microcontroller
11. While merely illustrative of a processor suitable for
implementing the invention in one form, this microcontroller has an
internal clock, a microprocessor, a self contained eight bit analog
to digital (A/D) converter, 256 bytes of random access memory
(RAM), 512 bytes of electronically erasable programmable read-only
memory (EEPROM). An additional 16 Kilobyte erasable programmable
read-only memory (EPROM) or other programmable read-only memory
(PROM) 13 is also included for fixed subroutines. The internal
clock may provide a 4 megahertz pulse train as shown (not to scale)
in FIG. 3d. The repetition rate of this clock signal greatly
exceeds that of the others depicted in FIG. 3 and, if drawn to
actual scale, would appear to paint the entire region. Power for
the system is provided by a 250 volt pulsed magneto 10 the output
of which is converted by a power converter 15 which includes a full
wave rectifier 17 and a DC to DC converter 19 which provides a five
volt source of the electronic circuits. Magneto 10 may be a Bendix
S1800 Series magneto available from applicants' assignee. The
output of the full wave rectifier 17 is used to charge capacitors
21 and 23 which form a part of a capacitor discharge ignition. A
nine volt battery 25 to provide power when the engine is not
operating or during low RPM operation when the output of the
magneto 10 is inadequate to supply all the electrical need s to the
ignition system. Engine speed is measured by a sensor 27 which
provides a pulse train of, for example, 60 pulses for each
revolution. This pulse train is depicted in FIG. 3c. A second
sensor 29 provides a reference pulse once each revolution as
depicted in FIG. 3b, and the two pulse trains together provide an
indication of current crankshaft position. For a two-stroke-cycle
engine, an ignition pulse is provided to each cylinder once for
each crankshaft revolution while a four-stroke-cycle engine
cylinder requires an ignition pulse only once every other
revolution. A cam reference input signal is provided on line 31 so
that the controller can distinguish between the power and exhaust
strokes during four-stroke-cycle operation. The cam reference
signal is a pulse train as shown in FIG. 3a having a repetition
rate which is half that of the signal on line 40 from crankshaft
sensor 29. Such cam references are usually achieved by placing a
sensor in close proximity to the engine cam shaft, however, in the
present invention, the power unit 10 is coupled to the engine
crankshaft with a two-to-one gear reduction and a sensor 38 detects
each rotation thereof providing the desired pulse train.
In FIG. 3a, a pulse occurs once for every other revolution of the
crankshaft while in FIG. 3b, a pulse occurs once for each
crankshaft revolution. In FIG. 3c there would actually be, for
example, sixty pulses between T0 and T3 corresponding to the number
of holes or studs around the flywheel 16. At T0, a count of the
pulses in FIG. 3c is initiated. When this count reaches a
calculated value (two as illustrated) at time T1, a count of the
clock pulses in FIG. 3d is initiated. When this count reaches a
second calculated value at T2, a specific spark plug is energized.
For four-stroke-cycle operation, there is not count of the FIG. 3c
pulses initiated at T3 because of the lack of a pulse in FIG. 3a.
In actual practice, the count does continue, but is simply no reset
or initiated unless there is a CAMREF signal. The illustrated cycle
runs from T0 on the left to a second T0 at the right when it begins
to repeat. Modification of the desired count between T1 and T2
provides a very accurate change in timing.
An analog input which selectively retards timing is provided from
the control 33 on line 35. The control may be indicative of speed
changes or other parameters which would indicate timing retardation
as being desirable. This feature allows the power cylinder peak
pressure to be maintained close to optimum. As designed, the retard
range is user programmable with the analog signal varying in the
range of 4 to 20 milliamps. A pair of ten position rotary switches
33a and 33b are also provided to allow independent operator
adjustment of two different ignition timing modes in program
determinable steps. The availability of two different timing modes
may be desirable, for example, when transfers ware made between
fuels, or when step load changes are introduced. These two timing
schedules (called A and B) can be programmed independently. Each
can be programmed to be constant with speed, or to follow any
selected timing vs. speed curve. For example, timing can be
retarded during start for turbocharge operation. Then the start-run
crossover speed timing could be programmed to switch to a fixed
advanced position or could follow a more complex curve. Schedules A
and B can be offset (the timing either advanced or retarded) from
their programmed values by the switches 33a and 33b. Schedules A
and B can also be retarded by an external analog signal on line 35
with the range of retardation being user programmable. Any change
introduced by this signal is in addition to those caused by the
program or by the switches 33a and 33b. The operator may select
between the two different ignition timing modes by properly
positioning the switch 37 which provides a controller input on line
39 and may shut down the processor by actuating switch 41 providing
a signal on line 43. A further pair of switches 57 and 59 are
provided to allow an operator to enable the processor under power
of the battery 25 if some sort of engine status is required while
the engine in quiescent or to allow programming of the processor
via the RS232 port 45. The external logic inputs on lines 39 and 43
are logic discrete type inputs and are periodically poled by the
processor 11.
When the ignition system is not in operation, a conventional
lap-top or similar computer may be connected to the RS232 serial
interface (I/F) 45 and internal transceiver 47 which allows the
operator to communicate with the ignition processor i much the same
way a conventional lap-top or similar compute may be connected in a
network or by MODEM to bulletin boards, commercial databases and
the like.
The output from the ignition system is by way of a total of sixteen
possible isolated ignition drivers, eight from each of the eight
channel output drivers 49 and 51. Capacitors 21 and 23 are
alternately discharged through one of the step-up transformers such
as 26 when an individual spark plug driver such as 50 receives an
enabling signal on an input line such as 52. The system is designed
to have a maximum spark duration of 1000 microseconds during
start-up and to transfer to a shorter program determined spark
duration at a program determined speed. Two additional discrete
logic outputs are provided on lines 53 and 55. These outputs are
programmable to provide indications of various engine status or
fault conditions. For example, when an overspeed threshold is
exceeded, ignition may be interrupted shutting down the engine and
a indication provided by way of a signal on line 55. Alternatively,
fuel supply may be interrupted by a signal on line 53 while
ignition remains on so as to burn residual fuel prior to shut-down.
A four digit liquid crystal display 61 for displaying input
parameter and system programming data during programming of the
processor as well as normal status or cyclic error codes during
engine operation. For example, the display may repeatedly cycle
through indications of the commanded firing angle, the engine RPM,
which of the two selectable programs (A or B) is in effect, and a
measure of the current into the analog (four to twenty milliamp)
input 35.
The technique by which a fuel ignitting spark is provided at a very
precisely determinable time in the engine cycle is most easily
understood by considering the FIG. 3 waveforms. FIG. 3b shows an
engine rotation determined pulse train having a repetition rate the
same as the number of revolutions per second of the engine. This
pulse train is generated by sensor 29 and provide a pulse which is
indicative of engine crankshaft position. The repetition rate of
this pulse train is speed dependent at one pulse per revolution. A
second engine rotation determined pulse train is shown in FIG. 3c
which has a repetition rate which is an integral multiple of that
of the first pulse train. This pulse train is series of pulses
indicative of engine speed. With sixty holes such as 32 or 34
around the flywheel, the repetition rate of the FIG. 3c pulse train
is numerically the same as the engine RPM. The internal clock in
the processor 11 provides a third pulse train depicted in FIG. 3d
(not to scale) the repetition rate of which is significantly higher
than that of the second pulse train and is independent of engine
speed. The reference pulse may be utilized to initiate a count of
pulses in the second pulse train and, upon reaching a preselected
count, a count of pulses in the third pulse train is initiated.
When the prescribed third pulse train count is attained, the spark
plug is energized. Because of the very high repetition rate of the
third pulse train (e.g., 4mhz.) the precise time (count) after
occurrence of the last of the pulses in the second pulse train can
be extremely accurately controlled. Typically, the engine is a
multi-cylinder engine having at least one spark plug for each
cylinder and the pulses in the second pulse train are counted to
different preselected counts of different cylinders, thereby
enabling a different spark plug for each different preselected
count. At least two different desired values for the third pulse
train preselected count may be stored with each indicative of a
desired time for energization of the spark plug, and either stored
value may be manually modified to optionally manually fine-tune the
time at which the spark plug is enabled.
From the foregoing, it is now apparent that a novel arrangement has
been disclosed meeting the objects and advantageous features set
out hereinbefore as well as others, and that numerous modifications
as to the precise shapes, configurations and details may be made by
those having ordinary skill in the art without departing from the
spirit of the invention or the scope thereof as set out by the
claims which follow.
* * * * *